This invention relates generally to opthalmological surgery devices, more specifically, to a device and method for enhancing the visualization of corneal topography.
In corneal surgery, particularly photorefractive keratectomy (PRK), the surgeon determines the corneal topography to assess the effective corneal ablation. For example, the surgeon can use rastostereography for imaging a corneal surface or ablation test surfaces. A method of using rastostereography to evaluate the effect of a surgical laser on the cornea or test substrate is disclosed in my co-pending application Ser. No. 08/055,578, filed May 3, 1993 which is hereby incorporated by reference. Furthermore, the use of a Placido-disc videokeratoscopy to evaluate a surgical laser is disclosed in my co-pending application Ser. No. 08/269,139, filed Jun. 30, 1994, and entitled Method of Evaluating a Laser Used in Ophthalmological Surgery, also incorporated herein by reference.
In such procedures, a grid or concentric circle image is projected onto the cornea. The image is captured with a video frame-grabber and then analyzed by a computer to determine the topography of the cornea. Such analysis informs the surgeon of the elevations and depressions on the corneal surface. As disclosed in the above referenced applications, the surgeon can use the rastostereography or videokeratoscopy prior to laser ablation of a test substrate and then after ablation to evaluate the effect of the laser on the substrate. Moreover, the surgeon can perform rastostereography or videokeratoscopy procedure on the cornea before and after surgical ablation of the cornea to determine whether or not there are high or low elevations. That is, the topographical analysis will inform the surgeon of any "hot" or "cold" spots on the cornea.
Prior art methods of using rastostereography, for example, are limited by the need to use a fluorescein dye in order to adequately capture the grid projected on the cornea. The use of fluorescein dye can cause inconsistencies and unreliable results. The variable thickness of the liquid dye layer on the surface of the cornea can be a problem. Moreover, corneal surfaces, particularly immediately after ablation, absorb some dye. Absorption causes a variable thickness of the dye layer on the ablated cornea surface. Furthermore, the fluorescein dye can interact with ultra-violet laser energy resulting in inconsistent and unpredictable laser energy absorption and ablation of the tissue, and disrupt the accuracy of the entire surgical procedure.